The present invention relates to a multi-output DC-DC converter.
Multi-output DC-DC converters are known in the art. As shown and described in J. Sevastian, J. Uceda and F. Aldana, "New topologies of Fully Regulated Two-Output DC-to-DC Converters with Small Frequency Variation Range", I.E.E.E. PESC '86 Record, page 266, FIG. 5, a bipolar transistor is used for periodically switching an input DC voltage. First and second rectifier-filter circuits are provided. The first rectifier-filter receives the switched DC voltage through a resonant circuit to generate a first DC output voltage which varies at least as a function of the frequency at which the transistor is switched, and the second rectifier-filter receives the switched DC voltage direct to generate a second DC output voltage which varies at least as a function of the duration, or conduction period of the transistor. Deviations of the first and second DC outputs from a reference voltage are sensed and used to control the switching frequency and conduction period of the transistor to maintain the output voltages constant under varying input voltage and load current conditions. However, one drawback of the prior art is that, due to the speed limitations of the bipolar transistor, desired high speed switching cannot be achieved to generate high frequency oscillations. Another disadvantage is the delayed response of the transistor at the trailing edge of the switching pulse due to a current through a circuit connected in parallel with the transistor. As a result, the control range of the prior art multi-output DC-DC converter is not sufficient to cover the range of input-voltage and load-current variations.